Effect of Photosynthetic Photon Flux Density on Strawberry Runner Tips Propagated Indoors

Abstract

Controlled-environment systems that use sole-source lighting can facilitate year-round production of strawberry (Fragaria 3ananassa) transplants, but optimal propagation conditions indoors are largely unknown. Therefore, the objective of this study was to compare growth, physiological responses, and yield of strawberry runner tips propagated indoors under different photosynthetic photon flux density (PPFD) treatments. During a propagation phase that lasted 28 days, runner tips from two crown diameters (small crown diameters were <10 mm, and large crown diameters were >10 mm) of ‘Albion’ and ‘Fronteras’ were grown indoors under 75, 150, 225, or 300 ± 5 lmol·m-2·s-1 provided for 24 h·d-1 by broadband white light-emitting diode fixtures. Runner tips were also grown in a shaded greenhouse under mist, which was used as a control treatment. A finishing phase lasting 7 weeks was conducted in a greenhouse to evaluate carryover-treatment effects. In general, the two cultivars followed similar treatment responses, whereby biomass production increased in response to higher PPFD indoors, despite increases in the percentage of dead shoots and decreases in gas exchange and chlorophyll concentration, likely caused by radiation stress. Ultimately, however, there were no growth or yield benefits from increasing PPFD during indoor propagation, because there was a general lack of treatment response after the carryover finishing phase. In addition, although there were several growth advantages when using 225 or 300 lmol·m-2·s-1 indoors compared with propagating plants in the greenhouse, differences were negligible during the finishing phase. Therefore, propagating runner tips of ‘Albion’ and ‘Fronteras’ indoors under 75 mmol·m-2·s-1 or in a greenhouse under mist should be adequate. Nonetheless, providing higher PPFDs could potentially reduce the rooting cycle during indoor propagation, because plants under 300 lmol·m-2·s-1 had more root coverage at 18 days than those under 75 lmol·m-2·s-1 at 28 days.